The present invention relates generally to an injection molding apparatus, and in particular to a manifold having a valve pin guiding device that acts as a flow restriction.
Manifold plugs or inserts for manifolds are well known in the injection molding industry. In applications that require the use of a movable pin to regulate the flow of a molten material, these manifold plugs are also referred to as valve pin bushings. During injection molding, the manifold plug receives a melt stream of moldable material from a manifold and delivers the melt stream to a nozzle via a manifold plug channel provided in the manifold plug. The manifold plug channel is typically elbow shaped. As a result, the melt stream must follow an approximately 90 degree bend between the inlet of the manifold plug channel and the outlet thereof. Reference is made in this regard to U.S. Pat. No. 4,017,242; U.S. Pat. No. 4,299,553; U.S. Pat. No. 4,609,138; U.S. Pat. No. 5,295,806; U.S. Pat. No. 5,366,369; U.S. Pat. No. 5,441,197; U.S. Pat. No. 5,762,976; U.S. Pat. No. 5,955,121; U.S. Pat. No. 6,007,108; European Patent Document No. 0 845 345; and European Patent Document No. 0 875 355.
In the case of an injection molding apparatus having a valve pin operated to control the melt stream flow through the manifold or a hot runner nozzle, the manifold includes a bore that extends therethrough to accommodate the valve pin. In some cases, the bore is located in the manifold plug or insert. The valve pin is actuated by a valve piston, or by any other appropriate mechanical or electrical device. The actuation device is typically located above the manifold bore and the valve pin is slidable through the manifold or the manifold plug bore. As the melt stream flows through the manifold channel or manifold plug channel, a continuous force is applied to the valve pin. The direction of the force is generally perpendicular to the longitudinal axis of the valve pin, and therefore the valve pin experiences bending stresses as a result.
Extending a valve pin through a manifold or a manifold plug causes a dead spot or pin shadow to be formed behind and/or downstream of the valve pin, between the valve pin and the inner wall of the manifold channel or manifold plug channel. A dead spot is a location where moldable material from the melt stream slows down and becomes trapped. This area therefore has a stagnant flow pattern, which affects the performance of the manifold. Dead spots are undesirable particularly for color change applications because the number of cycles required to flush out the old color is increased.
U.S. Pat. No. 5,374,182 to Gessner discloses a hot runner manifold bushing that does not accommodate for the formation of dead spots behind the valve pin. Reference is also made to U.S. Pat. No. 3,716,318; U.S. Pat. No. 4,781,572; U.S. Pat. No. 4,932,858; and U.S. Pat. No. 5,811,140 that teach various valve bushing designs.
It is therefore an object of the present invention to provide a restriction or a guide for a manifold or manifold plug channel, which obviates or mitigates the above disadvantages.
According to one aspect of the present invention there is provided An injection molding apparatus comprising:
a manifold having a manifold channel for receiving a melt stream of moldable material under pressure;
a manifold plug provided in said manifold, said manifold plug having a manifold plug channel formed therein, said manifold plug channel having an inlet receiving the melt stream from said manifold channel and an outlet delivering the melt stream to a nozzle channel of a nozzle, said manifold plug channel undergoing a change in direction between said inlet and outlet;
a mold cavity receiving said melt stream from said nozzle, said nozzle channel communicating with said mold cavity through a mold gate;
a valve pin passing through a bore provided in said manifold plug and extending into said manifold plug channel and said nozzle channel, said valve pin being movable to selectively open and close said mold gate; and
a guide projecting from an inner wall of said manifold plug channel, diametrically opposing said inlet, said guide being located behind said valve pin and abutting a portion of said valve pin.
According to another aspect of the present invention there is provided a manifold plug comprising:
a manifold plug body including a manifold plug channel having an inlet and an outlet formed therein;
a guide body projecting from an inner wall of said manifold plug body diametrically opposing said inlet, said inlet for aligning with a manifold channel of a manifold and said outlet for aligning with a nozzle channel of a nozzle, said inlet being at an angle to said outlet; and
a guide surface provided on said guide body, said guide surface abutting a downstream portion of a valve pin extending through said manifold plug body.
According to yet another aspect of the present invention there is provided an injection molding apparatus comprising:
a manifold having a manifold channel for receiving a melt stream of moldable material under pressure and delivering said melt stream to a nozzle, said manifold channel undergoing a change of direction from an inlet to an outlet and being aligned with a nozzle channel of said nozzle;
a mold cavity for receiving said melt stream from said nozzle, said nozzle channel communicating with said mold cavity through a mold gate;
a valve pin extending through a bore provided in said manifold and through said nozzle channel, said valve pin being movable to selectively open and close said mold gate;
a guide projecting from an inner wall of said manifold channel, said guide being integrally formed with the inner wall of said manifold channel and diametrically opposing said inlet for facilitating flow of said melt stream, said guide being located behind said valve pin and abutting a portion of said valve pin.
The present invention provides advantages in that the occurrence of dead spots behind the valve pin is reduced and the valve pin is provided with additional support and guidance so that it is less susceptible to bending.